1) Field of the Invention
The present invention relates to growth substrates which predominantly consists of mineral wool fibres formed into a coherent matrix and mutually bonded by a cured binding agent and if appropriate impregnated with a wetting agent for rapid water uptake before use. These mineral wool fibres may be stone wool fibres, glass fibres, slag fibres and the like.
2) Description of the Prior Art
The air and water distribution within the growth substrate is dependent on the hydraulic pressure over the height of the growth substrate, but also dependent on the internal surface.
The internal surface is a function of the density of the growth substrate, of the fibre diameter of the mineral wool fibres used and of the content of non-fibre material (shot).
Growth substrates have a total density within the range of 5-200 kg/m.sup.3, preferably between 20-180 kg/m.sup.3, more preferably 40-120 kg/m.sup.3, and practically 50-70 kg/m.sup.3.
The fibre diameter is normally within the range of 1-20 micrometer, preferably 2-10 micrometer, such as 3-8 micrometer.
The amount of shot varies between 0-50 Wt % such as 0-40 Wt %. For stone wool it is normally 30-35 Wt % and for glass wool it is 5-10 Wt %.
Furthermore the aspect ratio (length over diameter ratio) is normally less than 5 for shot.
The value for the internal surface varies between 5,000 and 20,000 m.sup.2 /m.sup.3. A high internal surface is in the range of 16,000-20,000, low in the range of 5,000-8,000 and moderate in the range of 9,000-15,000 m.sup.2 /m.sup.3.
The invention has for its object to provide new growth substrates which possess better properties, such as a better water distribution, a better air distribution, a better root penetration and distribution, and further a better compression or bending strength.